1. Field of the Invention
The present invention relates to a new antenna architecture used for. More specifically, an antenna architecture for the reception of tri-band and quad-band RF signals is disclosed.
2. Description of the Prior Art
The demand for wireless data services has become a critical part of life in modern society. Increasing numbers of users demand wireless capabilities of Internet access, email communication, video conferencing, and multimedia applications and make a wireless PDA (Personal Data Assistant) or a Smart Phone suitable devices to provide the data rates necessary for the new multimedia services.
In order to fulfill the customer's demand for wireless data services, multimedia devices such as PDAs and smart phones must provide a network that not only supports various content but also provides it in a seamless system that customers can rely on anywhere and anytime.
Take the most popular Global System for Mobile Communications (GSM) systems for example, the GSM systems are being standardized with specific frequency spectrums including 850 MHz, 900 MHz, 1800 MHz, and 1900 MHz. The lower two frequency spectrums are the oldest and most commonly used throughout the world. The 1800 MHz frequency range, or GSM 1800 (also called DCS 1800 and PCN (Personal Communication Network)) is found in an increasing number of countries throughout Europe and Asia. The 1900 MHz range, or GSM 1900 (also called DCS 1900, PCS 1900, and PCS (Personal Communication Services)) is used in the United States and Canada for GSM. A mobile unit with a tri-band or quad-band antenna architecture enabling clear sending and receiving of these different frequency spectrums holds a large commercial advantage of being compatible with more wireless data and multimedia systems.
The details of the factors influencing antenna design are well known in the art and need not be elaborated here. The efficiency of any antenna lies in a proper relationship between the size and shape of the antenna and the wavelength of the targeted frequency. As the number of targeted frequency ranges increases for any given antenna, the less efficient the antenna becomes. While a single-band antenna will nearly always outperform a dual-band antenna, acceptable results can be achieved in a properly designed dual-band antenna if the targeted frequency ranges are reasonably similar, for example 850 MHz and 900 MHz. Because optimum antennas for similar frequencies are of similar sizes, a good impedance match over both frequencies is possible and the Voltage Standing Wave Ratio (VSWR) affecting efficiency can be kept within reasonable limits of perhaps 2:1. On the other hand, if a single antenna is used with different, substantially non-harmonic frequencies, it is impossible to get a properly sized and impedance matched antenna for both frequency ranges and the VSWR climbs, rapidly reducing gain.
The specific frequency range that the antenna is designed to cover dictates the optimum size of an antenna. If the intended frequency range is too large or inappropriate for the antenna, signal reflections interfere with proper antenna functioning, result in loss of gain, and require additional power for adequate transmission or reception. Most mobile units are battery operated, cannot easily afford to waste power, and are consequently equipped with antennas properly matched for the intended frequencies. Therefore, a conventional mobile unit with properly tuned antenna can cover only a relatively narrow range of frequencies efficiently.
The mobile antenna architectures most commonly used today are of a planar type or a whip type and both perform well in dual-band roles. However, attempting to turn either type into a tri-band or quad-band antenna to utilize the four GSM frequencies enumerated above presents serious problems. First, a tri-band or quad-band antenna suffers from a high VSWR due to accommodating the required spectrums and bandwidths. Second, the high VSWR results in a low average gain, placing additional power concerns upon the mobile unit. Thirdly, a large size or a bad cosmetic design result if two planar or two whip structured antennas are used to accommodate the required frequency ranges.
Because of the drawbacks listed above, the current antenna architecture is neither feasible for wireless PDA or Smart Phone product development nor able to pass the output power and sensitivity test required by the GSM standard.